Under-house Excavation on the Sunshine Coast

What under-house excavation on the Sunshine Coast actually involves

The planning scheme's acid sulfate soils overlay maps land at or below 5 metres AHD as Area 1 and land above 5 metres and below 20 metres AHD as Area 2, the areas potentially subject to acid sulfate soils. Where the code applies to the work, its aim is to avoid disturbing acid sulfate soils when excavating or removing soil, or to treat them if they are disturbed. Sunshine Coast Council explains that these soils are harmless when undisturbed, but once dug up or drained they meet oxygen and can produce sulphuric acid, which can damage buildings, roads and other structures. On a low coastal block, ask whether the lot is on that overlay before anyone digs.

What is in the ground, and where it goes

Then there is the spoil. QBCC notes reports that some builders have been charging excessively for earthworks and footings, says a builder must provide a soil test and contour survey to justify those costs, and tells owners to check the quote or contract to confirm who is responsible for removing excess soil, as this can be an expensive addition.

Timing and drainage are local as well. The Bureau of Meteorology's record for Sunshine Coast Airport shows a mean of 217.5 mm in February and 51.1 mm in September, and its older Nambour record shows 259.1 mm and 49.2 mm. Open excavation is easier to schedule in the drier months. On the flat coastal plain, where the Bureau notes flooding lasts longer, lowering the floor of a space creates a low point in ground where water already leaves slowly, so get the flood level and freeboard from the flood information search before anyone decides how far down to dig.

Under-house Excavation on the Sunshine Coast — common questions

How much head height can I gain?

It depends on how high the house sits now and how far down you can go before drainage or footings become the constraint. A dig-out is usually paired with a raise for that reason — raising gains height from above, excavating gains it from below.

Why does retaining come with a dig-out?

Because an excavated edge under a house has to be held. Council lists retaining walls over 1m in height, or within 1.5m of a building or another retaining wall, as needing a development building work permit.

Can spoil be spread on my block?

Not without checking what the soil is. QBCC tells owners to check who is responsible for removing excess soil, and the planning scheme's code is about not disturbing acid sulfate soils, or treating them if they are disturbed.